Wind and water-driven devices have been used for centuries for conversion of naturally occurring phenomena into useful power. Advances in aerodynamics and materials science have increased the efficiency and decreased the weight and friction of these devices, and concomitantly increased their usefulness. Turbine blades have progressed from primitive paddle wheels to space-age shapes with complex compound curves that require sophisticated manufacturing techniques such as numerically-controlled laser cutting, composite molding, casting, and powder metallurgy. Until demand drives production to very high levels, such manufacturing requirements make high-efficiency turbines prohibitively expensive, particularly in developing nations where wind and water could provide much-needed power sources.